In the drilling, well completion, production, transport, storage, and processing of crude oil and natural gas, including waste water associated with crude oil and gas production, and in the storage of residual fuel oil, H2S and mercaptans are often encountered. The presence of mercaptans is objectionable because they often react with other hydrocarbons or fuel system components. Another reason that the H2S and mercaptans are objectionable is that they are often toxic and highly corrosive. H2S in aqueous environments can adversely affect the integrity of pipelines, separators, storage tanks, etc. by corroding the materials of construction. Even low levels of H2S in aqueous systems may be toxic to many living organisms. For instance, a trace amount on the order of 100 ppm may be fatal to humans. Still another reason that mercaptans are undesirable is that they have highly noxious odors. The odors resulting from mercaptans are detectable by the human nose at comparatively low concentrations and are well known. For example, mercaptans are used to odorize natural gas and used as a repellant by skunks and other animals.
The predominant H2S scavengers for natural gas and crude oil are monoethanolamine (MEA) and monomethylamine (MMA) triazines. These triazine compounds, which are amine/aldehyde condensates, contain nitrogen and when used in sufficient concentration can cause problems for certain refineries. Also, the relatively high dosage rates for these triazines, and hence the higher costs, make them less desirable. In addition, there are health, safety and environmental (HS&E) concerns with H2S scavengers that may contain formaldehyde. There have been instances where operators have required the use of a non-nitrogen containing H2S scavenger. Glyoxal and/or acrolein have been used as a H2S scavenger in these instances. Glyoxal is corrosive to mild steel. Acrolein is an extremely toxic substance which operators do not like to use.
Metal oxide (e.g. zinc oxide, ferrous oxide, etc.) solutions and caustic solutions (e.g. sodium hydroxide, potassium hydroxide, etc.) have also been used in the past. However, the metal oxide solutions may generate slurries and solids which have disposal issues, and the caustic solutions may be corrosive.
Hydroquinones are known to be useful as mercaptan scavengers. They are used, for example, with a basic solution to catalyze the oxidation of mercaptans to disulfides to regenerates solvent used for mercaptans exactions from crude oil. Even though hydroquinones have been widely used, their use has not been trouble free. For example, the hydroquinones require both a basic solution, such as caustic, and oxygen to be effective.
U.S. Patent Application Publication No. 2009/0095658 to Yang, et al. (Baker Hughes Incorporated) describes compounds having general formula:
wherein each R1, R2, R3 and R4 are the same or different and may be hydrogen, an alkyl group, an aryl group, a halogen, a nitro group, an alkyl or aryl ester, and an alkyl or aryl ether; and other compounds where one or two of R1-4 are quaternary ammonium moieties. These compounds can be used as additives for crude oil and hydrocarbons. These compounds are taught as useful to scavenge mercaptans, sulfides, cyanides, and primary or secondary amines; either alone or in combination. In this Publication, these compounds have been formulated in aprotic solvents such as, but not limited to, aromatic solvents, dichloromethane, chloroform, tetrahydrofuran, N-methylpyrolidone, dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and the like.
It would be desirable if new H2S and/or mercaptan scavengers were discovered which could be implemented in protic solvents, and which did not necessarily contain nitrogen.